Agitating mills of the kind described above are known. They all have the common feature that the major part of the driving energy for the agitator is converted into heat. In the vast majority of applications this heat is undesirable. In many applications the reason that certain materials cannot be ground in agitator mills of this kind is in fact because of the danger of overheating. On the other hand, in many such cases, if a good grinding effect is to be achieved, it is necessary to introduce considerable grinding energy into the mixture of material being ground and grinding elements.
It is known from German Pat. No. 1,211,906, for annular discs acting as agitator elements to be fastened eccentrically on the agitator shaft in an agitating mill, these annular discs being in the form of a helical surface. In this way it is intended to effect compaction of the grinding bodies, that is to say to improve the grinding effect by preventing the grinding bodies from passing exclusively into a suspended state in the stream of material being ground and grinding bodies.
In another form of agitating mill, known from German Pat. No. 1,214,516, a closed cylinder extends centrally within the entire length of the grinding vessel, and the grinding elements are disposed in the annular space formed by the outer wall of the cylinder and the inner wall of the grinding vessel. By this means, it is intended to ensure that as a result of their approximately equal distance from the agitator axis the grinding bodies will have approximately the same velocity, so that their comminuting action will be substantially equal. In this way, it is intended to avoid great differences in the fineness of the processed material.
In another form of agitating mill known from German Auslegeschrift 1,233,237, exchangeable inserted rings, bars or cylinders may be fastened on the inner wall of the grinding vessel and carry rods which are so disposed as to be situated between the rods of the rotating cylinder which serve as agitator tools. By this means it is intended to prevent the grinding bodies from rotating together with the material being ground, in which case the grinding bodies would no longer transmit to one another the impulses received from the agitator tools, which would result in decreased grinding output. The exchangeability of the rods serves to permit rapid cleaning.
An agitating mill is also known from German Auslegeschrift 1,276,985, which works as a friction mill, that is to say an agitator mill having a compact package of grinding bodies, in which mill the agitator consists of a cylindrical roller body which is provided with at least one annular projection of larger diameter. Particularly in friction mills this measure serves to provide an adequately large friction surface between the agitator and the grinding bodies which are not freely movable in the material being ground.
The problem sought to be solved by the present invention is that of so developing a stirring or agitating mill of the kind described above that, on the one hand, considerable grinding energy is introduced locally into the mixture of the material being ground and the grinding bodies, and that, on the other hand, good dissipation of heat is effected, particularly at these points.